It has been conventionally known to prepare monosilane, disilane or derivatives thereof by using an alkyl aluminum hydride. For example, in Japanese patent application Publication No. 36-517, British Pat. No. 823,483, German Pat. Nos. 1,055,511 and 1,117,090, there is disclosed a process for preparing a silicon hydride by the reduction of a silicon halide with sodium hydride in the presence of an alkyl aluminum hydride. In this known process, it is sodium hydride that serves as reducing agent for the silicon halide, and the alkyl aluminum hydride is added in such a small amount as 0.1-30% so that it serves only as an activating agent.
Another process for the reduction of a silicon halide is disclosed in French Pat. No. 1,499,032, in which the reducing agent consists of an alkyl aluminum hydride only.
These processes, however, are not yet satisfactory in that the yield of end products is lower and high quality is not obtained.
From the industrial standpoint, it is more advantageous to utilize an alkyl aluminum hydride in the form of a mixture of said alkyl aluminum hydride and a trialkyl aluminum rather than as pure alkyl aluminum hydride, since such a mixture is commercially available at a low price. However, when the reduction of a silicon halide is conducted using such a mixture of alkyl aluminum hydride and trialkyl aluminum, there is an extremely low yield of a silicon hydride, together with a large amount of by-produced silicon halide hydride, for example, monochlorosilane SiH.sub.3 Cl, which is probably produced because of insufficient reduction of the silicon halide. In addition, there is produced a large amount of ethane as by-product.
An object of the present invention is to provide a process for the preparation of silicon hydrides with improved yield and reduced amount of by-products without lowering the activity of alkyl aluminum hydride by using a mixture of an alkyl aluminum hydride and a trialkyl aluminum which is easily available as the reducing agent for silicon halides.